move a vertex to the position of another vertex (different object) in python?
I wrote this example script for you. Mind the comments. 

import bpy
import bmesh

# Get the coordinates of the first vertices of 'Plane' object
firstObjData = bpy.context.scene.objects['Plane'].data
bm1 = bmesh.new()
bm1.from_mesh(firstObjData)

bm1.verts.ensure_lookup_table()

# Convert local coorinates to world coordinates before assignment
vertCoordinates = bpy.data.objects['Plane'].matrix_world * bm1.verts[0].co.xyz

print(vertCoordinates)

# Set the coordinates of the first vertices of 'Cube' object
secondObjData = bpy.context.scene.objects['Cube'].data
bm2 = bmesh.new()
bm2.from_mesh(secondObjData)

bm2.verts.ensure_lookup_table()

# Convert world coorinates to local coordinates before assignment
bm2.verts[0].co.xyz = bpy.data.objects['Cube'].matrix_world.inverted() * vertCoordinates 

bm2.to_mesh(secondObjData)